RRRRRRRR-RING! The Memovox’s alarm sounds like the ringing of an old telephone. The volume isn’t earsplitting on the wrist, where it unobtrusively reminds its wearer of an upcoming appointment. But when this watch is placed on a bedside table, the tabletop becomes an additional resonating body and the alarm rings loudly enough to summon even the most somnolent sleepyhead from dreamland.

An alarm ranks among the most practical horological complications. And the Jaeger-LeCoultre Memovox, along with the Vulcain Cricket, is one of the best-known models with this audible feature. With a name that can be translated as “the voice of memory,” the Memovox first rang in 1950 (pictured above, left).

The collection has undergone numerous expansions over the years. For example, a model with time zones printed on its dial debuted in 1958 (pictured above, right), followed by a variation that reminded its owner to grab a few quarters and run out to feed the parking meter.

The Memovox’s success came quickly. Its wearers have included such celebrities as actor and film director Charlie Chaplin. And the Memovox Deep Sea made history (see image below) in 1959, when it premiered as both Jaeger-LeCoultre’s first divers’ watch and the world’s first divers’ watch with a built-in alarm.

The watch had an automatic movement, which replaced the formerly hand-wound caliber. And its alarm reminded a diver underwater that the time had come to begin ascending toward the surface.

For its next divers’ watch, which debuted as the Polaris Memovox in 1965, Jaeger-LeCoultre developed a threefold caseback to make the alarm more clearly heard underwater.

The Memovox celebrated the Swinging Sixties with cases in a variety of imaginative shapes.

The most complicated model with alarm premiered as the Master Grande Memovox with perpetual calendar and moon-phase display in the year 2000.

The company unveiled the Master Compressor Extreme W-Alarm with world-time display and an alarm that could be set to the nearest minute in 2007.

The classic Memovox is currently available in steel and in rose gold. Triangular indexes and dauphine hands recall their counterparts on the original version.

A blue Memovox is the newest model, although its color, indexes and hands were inspired by a version from the 1970s.

This version is manufactured in a limited edition of 500 watches, which can be purchased only in Jaeger-LeCoultre’s boutiques and on the brand’s website.

Manufacture Caliber 956 is responsible for the time display, the date indicator and the alarm function. The positioning of the audible components is a highlight in this construction. The automatic-winding rotor and the gong are essentially in each other’s way, but Jaeger-LeCoultre solves this problem by allowing the gong to run along the inside of the caseback.

The alarm’s hammer strikes against a pin, which extends from the center of the back, through the bearing of the winding rotor and into the movement. The clever trick: The pin passes through a recess in the bearing of the winding rotor on its way toward its rendezvous with the hammer. Thanks to the gong and the caseback as a resonating body, the Memovox emits a ringing sound that’s both unusually mellow and uncommonly loud for a wristwatch: RRRRRRRR-RING!